1. Field of the Invention
The present invention relates to a lens barrel in which at least two or more lens groups are moved in an optical axis direction as well as to an imaging device and a hand-held data terminal device incorporating such a lens barrel.
2. Description of the Prior Art
There has been a strong demand for an imaging device such as a digital still camera or a digital video camera (hereinafter, digital camera) to improve its portability along with photographic performance. In order to aim to satisfy the demand, Japanese Patent No. 4224051 discloses an imaging device which comprises a lens barrel incorporating a focal-length variable photographic lens system made of plural lens groups. Such a lens barrel is configured to be collapsed into a chassis of a camera at non-photographing and be moved out from the chassis so that the lens groups are positioned with appropriate intervals for photographing. This imaging device excels in portability owing to the collapsible lens barrel and can shoot a subject at a desired angle of field by changing a focal length.
However, there is a problem with such an imaging device in terms of positioning cam grooves for moving lens group frames. That is, in the imaging device the lens barrel includes cylinder elements for holding the lens groups and two cam grooves are formed in the inner wall of a middle cylinder rotatable around a fixed cylinder element and movable in optical axis direction. The two cam grooves are used for moving a front cylinder element holding a first lens group and a second lens group frame holding a second lens group, respectively. It is necessary to determine the positions of the two cam grooves appropriately. Meanwhile, aiming for improving portability of the device, the middle cylinder is required to be decreased in size so that the size of the inner wall thereof is limited. This may make it difficult to freely design the cam grooves. Furthermore, the there may be no freedom in which a system for moving the photographic lens system and each lens group is designed, which makes it hard to improve the photographic performance of the imaging device.
It is possible to provide two extendable nested rotary cylinder elements rotatable around the fixed cylinder element and movable in the optical axis direction for the first and second lens groups, respectively. In this case one cam groove is formed on an front end (object side) of one rotary cylinder element to move the first lens group while the other cam groove is formed in the other rotary cylinder element to move the second lens group. However, such a configuration leads to an increase in the size of the lens barrel by the additional rotary cylinder and its relative components.